immunology and transplantation

• Normal immune function


  • Recognition of "non-self" and "abnormal self"
  • Protection from pathogens (bacteria, viruses, etc.)
  • Surveillance for tumours
• Components of the immune system

  • Innate
  • Adaptive
• Innate immune system


  • Macrophage
  • Neutrophils
  • Complement and natural antibodies (IGM)
• Adaptive immune system


  • Dendritic cells (antigen presentation)
  • T cells (helper and cytotoxic T cell)
  • Natural killer (NK) cells (cytotoxic)
  • B cells (antibody generation and memory)
• Major histocompatibility complex (MHC)


  • MHC in humans called histocompatibility locus antigen (HLA)
  • These molecules imprint individuality on cells and are pivotal in the generation of immune response
  • HLA genes are very polymorphic (ie., there are many different variations possible at each gene locus)
• HLA class 1 molecules

  • Expressed by most somatic cells of body
  • Used to present peptides from internally processed proteins
  • If class 1 HLA molecules is associated with virus-derived protein then the cell is recognised as infected
  • Infective cell will be killed by cytotoxic T cells
• HLA class 2 molecules

  • Expressed by antigen presenting cell (APC) that constantly 'sample' their microenvironment
  • Used to present antigenic peptides derived from digested material (including pathogens, abnormal or foreign cells)
  • Used by antigen presenting cells (DCs etc) to present antigenic peptides derived from digested and processed material
  • Cell surface expression of a peptide derived from pathogen of foreign cell will stimulate a T cell immune response
• T cell


  • Receptor complex and co-stimulation requires 3 signals to activate the T cell
  • Cytotoxic T cell is a very effective assassin with many mechanisms (TNF-⍺, membrane busting proteins, trans-ligand apoptosis)
  • Activation (pathogen, alloantigen) - dendritic cell finds abnormal pathogen or cell from transplant and collect, process and present antigen to T cell, T cell has antigen-specific responses facilitated by interleukin 2 (IL2) leading to clonal expansion
• Key principles of transplant immunology

  • Rejection of transplant is directed at specific proteins called antigens
  • Rejection is donor specific
  • Rejection may be both Cell or Antibody mediated
  • Rejection exhibits 'memory' (ie., a 2nd similar transplant is rejected more rapidly and this results from the rapid generation of cytotoxic antibodies that recognise the transplant)
• HLA profiling


  • Preformed using molecular biological and serological techniques
  • The HLA tissue types of all patients on the Kidney Transplant waiting list is held on a central UK database and the 'best match' chosen when kidneys become available
  • Used to allocate kidneys but less important for other organs such as liver (less immunogenic)
  • If all HLA-A, -B and -DR loci are the same then it is a 0-0-0 mismatch
  • If they are all different then it is a 2-2-2- mismatch
• Immunosuppression treatment


  • Corticosteroids
  • Calcineurin inhibitors (CNI)- Tacrolimus
  • Anti-proliferative agents (mycophenolate mofetil (MMF))
  • Monoclonal and polyclonal antibodies (IL-2 receptor blockers, T cells, co-stimulatory molecules)
• Patient assessment for transplant

  • Age important (biological vs chronological)
  • Primary cause of renal failure
  • Co-morbid disease (cardiovascular disease, diabetes, etc.)
  • History of infections
  • History of tumours
  • Urological disease
• Additional investigations


  • Cardiac (exercise ECG, myocardial perfusion studies)
  • Angiography
  • Urodynamic studies
  • Tumour markers, imaging
• Types of transplantation


  • Cadaveric transplant (DCD = donated after cardiac death, DBD = donation after brain death)
  • Living related donor transplant (sibling, spouse, altruistic)
• Living-related donor transplants have become better long-term outcomes
• Transplant procedure


  Attachment of the kidneys to the iliac artery/vein, in the pelvic/lumbar region
• Criteria for a kidney transplant to go ahead

  • Blood group (ABO) compatibility
  • Immunological 'X-match negative'
• Immunological X-match


  • Checking for presence of HLA antibodies in the recipient of the transplant
  • Checked through serum of the recipient and some cells from the donor (often splenocytes), which are mixed together and a vital dye (can enter dead cells) is added to identify if they are X-matched status
  • Positive is when the dye can enter the cell, negative is when the dye doesn't enter the cell
  • Flow cytometry methods used
• Production of HLA antibodies (sensitisation)


  • If a person is exposed to a foreign HLA molecule they can produce an HLA antibody against this
  • Approximately 30% of patients on renal waiting list have anti-HLA antibodies
  • The specificity of these antibodies has to be defined
  • Highly sensitised patients exhibit high levels of cytotoxic antibodies to many HLA antigens that may be driven from previous transfusion, pregnancies, or previous transplantation
• Luminex HLA antibody detection

  • 100 different colour-coded polystyrene beads is a single wall are each coated with a selected class 1 or class 2 antigen or pool of antigens (for screening purposes)
  • The micro-beads are incubated with the patient's serum
  • The beads are washed and incubated with PE conjugated anti-human IGG antibody
  • The beads are washed again, and run on labscan 100tm (which assign assay reactivity and antibody specificity
• Importance of anti-HLA antibodies


  • Make a successful X-match less likely (long wait for transplant)
  • Can lead to antibody mediated rejection
  • Consider desensitisation/antibody removal or paired exchange transplant
• Types of rejection


  • Hyper-acute rejection
  • Acute rejection (cell or antibody mediated)
  • Chronic rejection
• Hyper-acute rejection


  • Occurs when the transplant carries antigens to which the recipient is already sensitised
  • Cytotoxic antibodies bind endothelial cells and include complement activation, platelet aggregation and intravascular thrombus formation
  • The transplant is often destroyed 'on the operating table'
• Acute rejection


  • Features: rise in creatinine, reduced urine output, tender transplant, fever
  • Things to check before deeming it as acute rejection: dehydration, renal obstruction, vascular catastrophe, drug toxicity
  • Treatment: high dose methyl prednisolone, change to more potent immunosuppressive agent or an increased dose, 'anti-T cell' antibody, plasma exchange (severe acute antibody mediated rejection)
• Chronic rejection


  • Features: progressive renal dysfunction, interstitial fibrosis and vascular disease of renal biopsy
  • Causes: recurrent diabetic nephropathy, interstitial fibrosis, vasculopathy
  • Pathogenesis: increased HLA mismatched, previous acute rejection, poor drug compliance, prolonged cold ischaemia time of kidney prior to surgery
  • Factors promoting graft failure: delayed graft function, cytomegalovirus (CMV) infection, age of donor and 'donor disease', poor blood pressure control, proteinuria
• Management of chronic rejection

  • No specific treatment available, most patients will eventually require dialysis and potentially a further transplant
  • Optimise immunosuppression, proactive treatment of BP, lipids, proteinuria
• Infective risk of immunosuppression

  • Bacteria (urinary tract infection, chest infection)
  • Viral (CMV, herpes virus, parvo virus, BK virus)
  • TB
• Tumour risk of immunosuppression

  • Tumours - incidence of all cancers increased
  • Skin cancers common
  • Post transplant lymphoproliferative disorder (PTLD)- secondary to infection with Epstein Barr virus
• Immunosuppressive drugs- side affects

  • Calcineurin inhibitors are nephrotoxic
  • Increased risk of diabetes
  • Hypertension
  • Osteoporosis
• immunosuppression treatment, corticosteroids kill lymphocytes, interfere with T cell activation and gene transcription, and it is a powerful anti-inflammatory agents
• calcineurin inhibitors inhibit T cell activation by interfering with intracellular signalling pathway
• anti-proliferative agents inhibit clonal expansion of T cells
• angiography is required for kidney transplant, as descent vessel are needed for anastomosis
• renal biopsy should be done before deeming post-transplant rejection as acute rejection:

  • CD3 markers (T cells), and CD68 markers (macrophages)
  • can cause tubular damage (tubulitis), vascular rejection
  • antibody mediated rejection can be seen through C4d staining, which shows where antibodies bound (like an immune footprint)
• dehydration should be checked through clinical examination, BP, weight
• renal obstruction should be checked through Ultrasound
• vascular catastrophe should be checked through doppler
• drug toxicity should be checked through tacrolimus levels
• high dose methyl prednisolone causes anti-inflammatory, kills lymphocyte
• ‘anti-T cell’ antibody causes increased risk of infection, tumours